Characteristics of superplasticity domain in the processing map for hot working of as-cast Mg–11.5Li-1.5Al alloy

Processing map for hot working of as-cast Mg-11.5Li-1.5Al alloy has been developed in the temperature range 200–450°C and strain rate range 0.001-100 s−1. The map exhibited a single domain with a peak efficiency of 65% occurring at 400°C and 0.001 s−1. Under these conditions, the material exhibited abnormal elongation. On the basis of the elongation, the grain structure, the apparent activation energy for hot deformation (95 kJ mole−1) and the peak efficiency of power dissipation (65% corresponding to a strain rate sensitivity of about 0.5), the domain is interpreted to represent superplasticity. At strain rates higher than about 10 s−1, the material exhibits microstructural instability, while at temperatures of 450°C and a strain rate of 0.001 s−1, grain boundary cracking is observed

High-temperature deformation behavior of a gamma TiAl alloy-microstructural evolution and mechanisms

The present investigation was carried out in the context of the internal-variable theory of inelastic deformation and the dynamic-materials model (DMM), to shed light on the high-temperature deformation mechanisms in TiAl. A series of load-relaxation tests and tensile tests were conducted on a fine-grained duplex gamma TiAl alloy at temperatures ranging from 800 degreesC to 1050 degreesC. Results of the load-relaxation tests, in which the deformation took place at an infinitesimal level (epsilon congruent to 0.05), showed that the deformation behavior of the alloy was well described by the sum of dislocation-glide and dislocation-climb processes. To investigate the deformation behavior of the fine-grained duplex gamma TiAl alloy at a finite strain level, processing maps were constructed on the basis of a DMM. For this purpose, compression tests were carried out at temperatures ranging from 800 degreesC to 1250 degreesC using strain rates ranging from 10 to 10(-4)/s. Two domains were identified and characterized in the processing maps obtained at finite strain levels (0.2 and 0.6). One domain was found in the region of 980 degreesC and 10(-3)/s with a peak efficiency (maximum efficiency of power dissipation) of 48 pct and was identified as a domain of dynamic recrystallization (DRx) from microstructural observations. Another domain with a peak efficiency of 64 pct was located in the region of 1250 degreesC and 10(-4)/s and was considered to be a domain of superplasticity.ope

Hot deformation behavior and processing maps of diamond/Cu composites

The hot deformation behaviors of 50 vol pct uncoated and Cr-coated diamond/Cu composites were investigated using hot isothermal compression tests under the temperature and strain rate ranging from 1073 K to 1273 K (800 C to 1000 C) and from 0.001 to 5 s1, respectively. Dynamic recrystallization was determined to be the primary restoration mechanism during deformation. The Cr3C2 coating enhanced the interfacial bonding and resulted in a larger flow stress for the Cr-coated diamond/Cu composites. Moreover, the enhanced interfacial affinity led to a higher activation energy for the Cr-coated diamond/Cu composites (238 kJ/mol) than for their uncoated counterparts (205 kJ/mol). The strain-rate-dependent constitutive equations of the diamond/Cu composites were derived based on the Arrhenius model, and a high correlation (R = 0.99) was observed between the calculated flow stresses and experimental data. With the help of processing maps, hot extrusions were realized at 1123 K/0.01 s1 and 1153 K/0.01 s1 (850 C/0.01 s1 and 880 C/0.01 s1) for the uncoated and coated diamond/Cu composites, respectively. The combination of interface optimization and hot extrusion led to increases of the density and thermal conductivity, thereby providing a promising route for the fabrication of diamond/Cu composites

Influence of homogenization on the processing map for hot working of as-cast Mg-2Zn-1Mn alloy

Processing maps have been developed for hot deformation of Mg-2Zn-1Mn alloy in as-cast condition and after homogenization with a view to evaluate the influence of homogenization. Hot compression data in the temperature range 300-500degreesC and strain rate range 0.001-100 s(-1) were used for generating the processing map. In the map for the as-cast alloy the domain of dynamic recrystallization occurring, at 450degreesC and 0.1 s(-1) has merged with another domain occurring at 500degreesC and 0.001 s(-1) representing grain boundary cracking. The latter domain is eliminated by homogenization and the dynamic recrystallization domain expanded with a higher peak efficiency occurring at 500 degreesC and 0.05 s(-1). The flow localization occurring at strain rates higher than 5 s(-1) is unaffected by homogenization

Hot deformation behaviour of as-cast Mg-2Zn-1Mn alloy in compression: a study with processing map

The deformation behaviour of as-cast Mg-2Zn-1Mn alloy in the temperature range 300-500 degreesC and in the strain rate range 0.001-100 s(-1) has been studied using processing maps. For obtaining the processing map, the variation of the efficiency of power dissipation given by [2ml(m+1)] where 'm' is the strain rate sensitivity, is plotted as a function of temperature and strain rate. The map exhibited a domain of dynamic recrystallization (DRX) occurring at 450 degreesC and 0.1 s(-1) which are the optimum parameters for hot working of the alloy. The material exhibits grain boundary cracking domain with a higher efficiency at temperatures higher than 450 degreesC and at lower strain rates. At strain rates higher than 3 s-1, the material undergoes flow localization which has to be avoided in mechanical processing for obtaining consistent properties

Characteristics of superplasticity domain in the processing map for hot working of as-cast Mg-11.5Li-1.5Al alloy

Processing map for hot working of as-cast Mg-11.5Li-1.5Al alloy has been developed in the temperature range 200 450degreesC and strain rate range 0.001-100 s(-1). The map exhibited a single domain with a peak efficiency of 65% occurring at 400degreesC and 0.001 s(-1). Under these conditions, the material exhibited abnormal elongation. On the basis of the elongation, the grain structure, the apparent activation energy for hot deformation (95 kJ mole (1)) and the peak efficiency of power dissipation (65% corresponding to a strain rate sensitivity of about 0.5), the domain is interpreted to represent superplasticity, At strain rates higher than about 10 s(-1), the material exhibits microstructural instability, while at temperatures of 450degreesC and it strain rate of 0.001 s (1), grain boundary cracking is observed

Processing map for hot working of as cast magnesium

The constitutive flow behaviour in hot working of as cast magnesium has been studied with the help of a processing map developed in the temperature range 300-550°C and strain rate range 0·001-100 s−1. The map, interpreted using the dynamic materials model, revealed that the material undergoes dynamic recrystallisation at 425°C and 0·3 s−1, which are the optimum parameters for hot working. Ai temperatures higher than 450°C and strain rates lower than about 0·1 s−1, wedge cracking occurs in as cast magnesium. The wedge cracking domain has a high efficiency of power dissipation (60%), whereas the dynamic recrystallisation domain has a value of 34%. At temperatures below 450°C and strain rates above 10 s−1, the material exhibits flow instability in the form of mechanical twinning. At higher temperatures and strain rates, instability is manifested by flow localisation

Hot deformation behaviour of as-cast Mg–2Zn–1Mn alloy in compression: a study with processing map

The deformation behaviour of as-cast Mg-2Zn-1Mn alloy in the temperature range 300-500°C and in the strain rate range 0.001-100 s−1 has been studied using processing maps. For obtaining the processing map, the variation of the efficiency of power dissipation given by [2m/(m+1)] where 'm' is the strain rate sensitivity, is plotted as a function of temperature and strain rate. The map exhibited a domain of dynamic recrystallization (DRX) occurring at 450°C and 0.1 s−1 which are the optimum parameters for hot working of the alloy. The material exhibits grain boundary cracking domain with a higher efficiency at temperatures higher than 450°C and at lower strain rates. At strain rates higher than 3 s−1, the material undergoes flow localization which has to be avoided in mechanical processing for obtaining consistent properties